Hormone-Behavior Adaptations in Arctic Birds

北极繁殖的鸟类在天气条件仍然极端（低温、下雪）的时候到达它们的筑巢地。 然而，短暂的北极夏季要求它们尽早开始筑巢，以利用短暂的丰富食物来喂养幼崽。 不遵守这一严格的时间表会导致繁殖成功率大幅下降。在北极极端条件下最大限度地提高生存和繁殖成功率的激素行为适应是这项建议的重点。 研究表明，睾丸激素和领土侵略之间的相互关系是多种多样的，特别是当鸟类到达北极繁殖地时。 在某些物种中，领土是非常短暂的，之后鸟类显然对睾丸激素的影响变得顽固。 其他的在整个繁殖季节都是领土性的，但是这些行为对睾酮激活的依赖性仍然不清楚。 四到七个北极繁殖雀形目之间的侵略行为显示不同类型的领土将进行比较。 还将确定睾酮与攻击行为模式的关系以及操纵睾酮水平的影响。 此外，这些物种将与它们在中纬度地区繁殖的近亲进行比较（即配对比较，以避免混淆与系统发育关系有关的问题）。 通过这种方式，可以确定不同类型的领土行为的生态基础以及与睾丸激素的相互关系，并表明北极繁殖鸟类的潜在专业化。 北极和中纬度地区物种的相同光谱将用于比较肾上腺皮质对压力的反应。 大量的数据表明，北极鸟类调节皮质酮的分泌，以响应标准化的捕获压力协议作为纬度和繁殖周期阶段的函数。 这被认为是一种适应，以允许领土行为和繁殖在面对潜在的压力条件。 北极和中纬度物种都将进行比较。 将在这些物种比较中确定对皮质酮治疗的行为和生理反应，以表明内分泌机制如何随纬度和其他生态因素而变化。 最后，实验室实验将评估中枢神经系统中睾酮（和可能的代谢物）和皮质酮受体的数量和分布。 这种独特的野外实验方法比较了北极和中纬度雀形目鸟类的领土行为类型、激素和压力的影响，以及最终大脑中激素受体的相关分布，不仅可以确定鸟类在北极繁殖的具体适应性，而且对脊椎动物的生殖过程的调节具有重要意义。

Arctic breeding birds arrive on their nesting grounds at a time when weather conditions may still be extreme (low temperature, snow). However, the brief arctic summer requires that they begin nesting as early as possible to take advantage of the ephemeral abundance of food to feed young. Failure to adhere to this rigid schedule results in drastically reduced reproductive success. Hormone-behavior adaptations that maximize survival and reproductive success under the extreme conditions of the Arctic are the focus of this proposal. It has been shown that the interrelationships between testosterone and territorial aggression are diverse, especially as birds arrive on the arctic breeding grounds. In some species territoriality is extremely brief, following which birds apparently become refractory to the effects of testosterone. Others are territorial throughout the breeding season, but the dependence of these behaviors upon testosterone activation remains unclear. Aggressive behavior of between four and seven arctic breeding passerines displaying different types of territoriality will be compared. Temporal patterns of testosterone in relation to patterns of aggressive behavior and the effects of manipulating testosterone level will also be determined. Additionally, these species will be compared with their closest relatives breeding at mid-latitudes (i.e. matched pairwise comparisons to avoid confounding issues relating to phylogenetic relationships). In this way it is possible to determine the ecological bases of different types of territorial behavior and interrelationships with testosterone, as well as indicate potential specializations of arctic breeding birds. The same spectra of species in the Arctic and at mid-latitudes will be used to compare adrenocortical responses to stress. Extensive data now indicate that arctic birds modulate the secretion of corticosterone in response to a standardized capture stress protocol as a function of latitude and stage in the breeding cycle. This is thought to be an adaptation to allow onset of territorial behavior and breeding in the face of potentially stressful conditions. Both arctic and mid-latitude species will be compared. Behavioral and physiological responses to corticosterone treatment will be determined within these species comparisons to indicate how endocrine mechanisms may vary in relation to latitude and other ecological factors. Finally, laboratory experiments will assess the number and distribution of receptors for testosterone (and possible metabolites) and corticosterone in the central nervous system. This unique approach of field experiments to compare types of territorial behavior in arctic and mid-latitude passerines, effects of hormones and stress, and ultimately the related distribution of hormone receptors in the brain will not only pinpoint specific adaptations for birds breeding in the Arctic, but will have significance for the regulation of reproductive processes of vertebrates in general.